The rapid spread of acquired immune deficiency syndrome (AIDS) among intravenous drug users has created an urgent need for syringes that cannot be reused. In many situations, injections are given to patients without carefully controlling access to syringes. The use of reusable syringes under those circumstances increases the risk of infection. An infection can occur whenever syringes that have been used previously, and which therefore are no longer sterile, are used to administer injections.
Of course, reusable syringes are suitable for administration of a vaccine or other injectable medicaments when the injections are performed by a professional staff in formal health care facilities. In a hospital environment, skilled personnel sterilize the syringe for reuse, refill the syringe with the appropriate medicament, and personally administer the injections. Furthermore, circulation of these syringes is managed and controlled.
However, there are times when it is necessary or more economical to administer injections outside a hospital environment. For example, it may be necessary to give injections to a large number of individuals over a short period of time, patients may be located in a developing country or in an area without convenient access to a hospital or medical personnel, or it may be desirable to permit injections to be administered to a patient at his or her home or while he or she travels. Under these circumstances, it is virtually impossible to prevent misuse of the syringes. Furthermore, it is much more difficult to ensure proper sterilization of the syringes, particularly if medicaments are administered by non-professional personnel.
It is also important to develop an easy method of manufacturing a syringe that cannot be reused. Even though the use of disposable syringes reduces the risk of infection, it is not economically feasible to replace reusable syringes with disposable syringes unless the disposable syringes are made in a relatively inexpensive manner. Unfortunately, single use syringes that have been developed often are expensive to manufacture, or are so bulky that the syringes are inconvenient to ship and store.
In order to ensure proper administration of an injection, it is important that the syringe be designed to allow aspiration to verify proper placement of the needle in the patient. Trained medical personnel confirm whether a needle is or is not in a blood vessel by aspirating prior to injection of a medicament. In aspiration, a negative or suction pressure causes the needle to draw material into the syringe from the patient. The person administering the injection then visually examines the syringe to see if any blood has been drawn into the syringe through the needle. If, for example, the injection should be administered intravenously, the presence of blood after aspiration indicates proper placement of the needle.
The goals of designing a syringe that can be aspirated and which cannot be reused appear to be in conflict. Disposable syringes that contain a prefilled vaccine delivery system typically have a squeezable body portion or other elastic receptacle. In these syringes, a positive pressure is applied on or by the receptacle to force the medicament out through the needle. In order to perform aspiration, however, a negative pressure is applied to the receptacle. Unfortunately, the negative pressure needed to aspirate the syringe also may be used to reform the elastic receptacle, allowing the syringe to be reused.
Therefore, there is a need for an inexpensive and easy to manufacture syringe that cannot be reused, but which can be used to perform aspiration.